How Processing Parameters can Affect Properties for PLA

[BenZMSE]

Hello All,
Below you will find a link to a PDF summary of a Senior Engineering Capstone done by students at Arizona State University. The title of our project was Design of Experiment: 3D Printing Parameters and their Effects on Tensile Properties of Poly(lactic) Acid (PLA). We're more than happy to answer any questions you may have about our project by PMing me on this forum. Thanks and enjoy.

https://drive.google.com/file/d/0B9S...it?usp=sharing

Thanks and enjoy,
Ben Zimmerman

[Flixtix]

This was a great read. Thanks for sharing Ben. Are you one of the students that did this project or the professor? How many students were involved, if you don't mind me asking?

Also, by "Fracture Strength", what exactly do you mean?

24 Full-Factorial experiment

- What does this mean? I'm sorry I'm not as smart as you guys.

Is anneal time and anneal speed different than normal print speed and extruder temperatures?

[BenZMSE]

Flixtix,
I'm one of the four students that worked on the project and we had about 11 weeks to complete the project.
Fracture strength is the amount of load that a sample can hold before it breaks. This is dependent on the cross sectional area. We used an ASTM standard (D638) for tensile testing, so our dogbone-shaped samples were of uniform cross-sectional area, allowing for easy comparison to other materials.

A 2^4 Full Factorial experiment takes four factors (print orientation, print speed, anneal temperature, anneal time) at two levels (high and low) and puts them together in all possible combinations. For example, one sample was printed at the horizontal print orientation, at 45mm/sec, annealed for 70˚C for 15 minutes in an oven. After testing, we were able to investigate which factors/parameters were the most influential on the strength of the part.

Anneal temperature and time are actually post-print processing techniques more commonly used in metals processing. Once our samples were printed, we placed them in an industrial furnace at the appropriate temperature (25˚C, 70˚C, 140˚C) for the specified length of time. Our samples were printed at 190˚C at the hot end of our printer.

Thanks for your interest and let me know if you have any more questions,
Ben

[Flixtix]

Thanks for clarifying Ben. Very interesting study. Did you guys get graded on it yet? Do you use 3D printers a lot Arizona State?

[Eddie]

Great study Ben. You've been written about

Arizona State Students Conduct Study On How to Make 3D Prints Stronger
http://3dprint.com/3388/study-how-to...ints-stronger/

[BenZMSE]

Haven't been graded yet, but we have our fingers crossed. This is actually the first project in the Material Science and Engineering program to use 3D printers, but a lot of the machine shops have getting some really nice ones on campus. I also know that the Bio-design Institute has a few that they use for research, but I'm not sure what that is exactly.
Eddie and Brittney, thanks for the great write up.

[KLucky_13]

Hello,
I'm also a engineering student (industrial chemical process engineer, KULeuven Belgium). I'm also experimenting with an DIY FDM printer in my free-time. I read your paper with great interest. I never tried heating the prints again after printing to make them stronger. But I have a few questions about your research:

1. How do you explain the stronger prints when printing with higher speeds? I would expect the opposite.

2. I came across your paper via this article: http://3dprint.com/3388/study-how-to...ints-stronger/

On this article they use a picture (at the bottom of the article) I'm not sure but I think it has nothing to do with your research? It looks like the result of acetone-bathing ABS.. It would be nice to see such smoothing on PLA, but I think this picture has nothing to do with heating up the finished print.

3. Did you make some kind of data-plot with temperature vs. stiffness? I really like the fact that it makes the material stronger but it would be nice to see the real optimum time at a certain temperature. Then it would be clear after how much time further heating would be pointless.

Very interesting topic guys. Maybe I'll try this out myself when printing stuff that need higher strength.

Greetings,

Kenny

[nglasson]

Higher print speed makes sense for higher strength as it makes the layer to layer bond at a higher temperature - there is less time for cooling between layers. Running the extruder hotter will also help make parts stronger for the same reason. Unfortunately there are down sides to printing fast and hot. The optimal settings are design dependant. What works best for a tensile test piece, won't necessarily work best for a frog or a cellphone case. Annealing sounds interesting but I suspect that unless your parts are flat, higher temperature annealing will make parts droop.

[BenZMSE]

Higher print speed makes sense for higher strength as it makes the layer to layer bond at a higher temperature - there is less time for cooling between layers. Running the extruder hotter will also help make parts stronger for the same reason.

This is the conclusion we came to as well.

The picture linked in the article is not representative of our samples or what annealing does to the surface finish. We found that our parts did warp slightly at the higher temperature (140˚C), but perhaps some bracing while annealing would help to reduce this. I also think that people who print more decorative vs. structural parts would be less likely to need a stronger part, so annealing isn't for every print.

I hope to get our full paper linked here as soon as it is approved by our professor to do so.